“A ridge of high pressure is expected to set up Christmas day onward, leading to light winds and poor dispersion,” atmospheric scientist Ranil Dhammapala said. “Typically a lot more woodstoves and fireplaces are used during holiday festivities.

“Unfortunately, the weather isn’t helping to prevent smoke from pooling in these communities. So steps need to taken to reduce wood burning activities.”

Dispersion is expected to worsen over Christmas and lead to poor air quality later in the week.

Ecology’s Stage 1 burn bans will continue at least until 4 p.m. on Friday, when they could be called off or extended.

The Stage 1 bans apply to the use of uncertified wood-burning devices (including wood stoves, inserts and fireplaces) built before 1990 and to all outdoor burning.

All outdoor burning – including residential, agricultural and forest burning – is prohibited.

Under a Stage 1, ban the use of uncertified wood-burning devices – including fireplaces, wood stoves and inserts – is prohibited unless they are a home’s only adequate source of heat.

Certified wood-burning devices and pellet stoves are allowed.

Ecology recommends burning hot fires using only clean, dry wood. No excessive smoke is allowed from any wood-burning device beyond a 20-minute start-up.

The burn bans do not apply on tribal reservations, where the U.S. Environmental Protection Agency has jurisdiction.